Advances in point-of-care testing can provide direct and immediate information on a patient's status, leading to faster stabilization of life-threatenin crises and more effective patient triage at the site of accidents and in emergency rooms. The need for detection of drug substances in their parent and/or metabolized forms has become an issue at the forefront of public health awareness. Immunoassay-based, on-site devices are currently used to quickly screen for the presence of drugs in biological samples. Although they provide fast and sensitive screening results, the specificity and sensitivity of immunoassays varies depending on the assay principle, the employed antibodies and the detected substance. They often generate false-positives and false-negatives. The overall goal of this proposal is to develop a non-invasive, non-instrumental colorimetric assay that accurately screens drugs in saliva at point-of-care testing with high sensitivity and specificity. The investigators propose a colorimetric detection platform with a portable paper-based microfluidic device to simultaneously screen trace amounts of drugs in saliva with high specificity. Methylenedioxypyrovalerone (MDPV) and Mephedrone are chosen as targets because they are of particular interest for those who work in the health and criminal justice fields. In the proposed platform, aptamers will be generated through Microfluidic-SELEX process and used to specifically bind MDPV or Mephedrone, achieving a better specificity than that of immunoassay-based assays to minimize false-positives. Then, exonuclease III will digest the target/aptamer bound complex and recycle the target, generating superior sensitivity to minimize false-negatives. Screening result will be reported through the use of gold nanoparticles and their aggregation based color change. By transferring this platform into a paper-based device, the investigators expect to perform simultaneous screening of two drug molecules at a few mg/L concentrations in mL volumes of saliva within 10 minutes by the naked eye. Upon the success of this pilot study, the investigators will generalize the platform for the simultaneous screening of almost any designer drug molecules newly appeared on the market in ml oral fluid within minutes in a single paper- based, disposable device. This project will promote the participation of undergraduate and graduate students to interdisciplinary research in chemistry, biochemistry, forensic and biomedical sciences while helping the PI to establish new collaborations, enhance the research environment at Florida International University and obtain strong preliminary results for future R01 competition.